Switch Epoxy to Vinylester, what influence on design

Discussion in 'Materials' started by nico, Apr 25, 2007.

  1. nico
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    nico Senior Member

    What is the influence of switching from epoxy to vinylester from a design point of view? I dont have much data on that. Particularly in terms of stiffeners geometry and to account for secondary bonding.

    Regards,

    Nico
     
  2. marshmat
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    marshmat Senior Member

    Not as strong. Cheaper.
    Afraid I can't say much more with the information given. Epoxies make a better bond with the reinforcing fibres, thus are stronger. Epoxies also make better secondary bonds. But without knowing what you're planning, it's hard to be more specific.
     
  3. waikikin
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    waikikin Senior Member

    Using vinlyester in place of epoxy may end up the same cost in materials if used in sandwich construction or close to it as when using heavier woven or stitched fabric, chopped strand mat must be interleaved between layers & to core- the choppy is pretty resin hungry & costs some labour(easy) to install & the boat will be heavier, if solid construction the epoxy job will be much more expensive. Vinyle & poly resins are generally easier to use inside a "working" day to acheive progress , but not always:) . Regards from Jeff.
     
  4. War Whoop
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    War Whoop Senior Member

    The vinylesters talking secondary bonding one should not forget they have a good chemical bond along with the mechanical while Epoxies are mostly mechanical also the esters lend themselves to standard gelcoat systems and are nearly twice as strong compared with the polyester cousins.

    In a room temperature environment "only" (cost and ease of use) the vinylesters win hands down now post cured epoxies a different deal.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Vinylester and epoxy are the answers for use with modern style fabrics and high modulus fibers, because both are high strength, high elongation resins.

    Typically vinylester elongates to about 5% before cracking, having a tensile strength of 11,800 psi (82 mPa). This means the interlaminate bonds are much tougher, because of its peel resistance.

    Epoxy is stronger still, with higher elongation (over 5%) and gap filling qualities, which help avoid void defects in layup. Tensile strength is typically 12,500 psi (86 mPa) and higher formulations are available. Epoxy has a higher resistance to chemicals and blistering then vinylester (which is also pretty good, especially compared to polyester) and has the highest peel strength of any of the usually resin systems. It's peel strength is so good that mat can be eliminated from the layup, insuring the highest glass or fiber content is possible. In fact you can achieve laminates stronger then stainless steel at one fifth of the weight with a well bagged, bi-axial, S-glass epoxy laminate.

    Chemically they are all "esters" War Whoop. Polyester and vinylester are catalyzed, linear (long chain polymer) molecules, where epoxy is an activated three dimensional (cross linked polymer) molecule, which is how it gets it's strength. Both vinylester and epoxy have good chemical and mechanical bonds, with epoxy having the stronger in both.

    From a design point of view, most shops will have little difficulty switching from polyester to vinylester, but the transition from or to epoxy will require equipment, material handling, methods, technique and procedural changes. This affects the design process in regard to scantlings, specifically laminate schedules and the cost effectiveness of the end product as a marketable item. Often weight and materials dictate a specific resin use or a racer's competitiveness can be can be compromised if the wrong resin is incorporated into the design. These are some of the complex, convolutions in comprise we must address in design. Generally speaking, vinylester can be used in most products, but if the highest weight to strength ratios are required, epoxy should be considered. Of course if wood is involved, epoxy has to be given a strong inclination as well.
     
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  6. War Whoop
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    War Whoop Senior Member

    One more thing the working time can be adjusted on Some of the vinylesters with the right Inhibitor out to like 20 hours,
    I have used about every system from the Old ICI Atlac 580-05A (Urethane) through the Dow line to the 470’s then when overseas the Hetron from Ashland /SIR (Saudi industrial resins) To a custom formula by a small company with a 12 drum reactor a couple blocks from my shop I use an Interplastic product now but may go back to the Dow/Ashland line and start with a neat resin base.
     
  7. JR-Shine
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    JR-Shine SHINE

    Excellent explanation:!: If it was designed for epoxy, you could end up with a part that is heavier and cost the same to build. Risk of shrinkage is nill with epoxy, not so with vinylester
     

  8. waikikin
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    waikikin Senior Member

    War Whoop makes a really valid point on the gelcoat so far as finish is concerned on a $ per meter sqared basis contact molded gelcoat beats priming & polyu by leaps & bounds, sure people argue against gelcoat for a few reasons but its still hard to beat for cost & quick repair & its "weight" is insignificant in most applications. Regards from Jeff:)
     
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